Low coherence interferometry (LCI) methods have been investigated for the detection of damage on coated and uncoated airfoils in advanced gas turbines, and in particular methods for implementing LCI for in situ inspection using borescope-type instrumentation. The work reported in this paper includes design of prototype instrumentation and some test results, as well as results using commercial instruments obtained on TBCs. LCI techniques can provide significant advance over currently employed visual inspection of gas turbine airfoils. The instrumentation provides a significant advance over currently employed visual inspection of gas turbine airfoils. For instance, with thermal barrier coatings (TBCs), these techniques allow the detection and quantification of incipient spalls, delamination, and changes in TBC porosity which typically go unnoticed with visual inspection methods. The methods are well suited for use with borescopes and thus provide a large potential to be developed into commercial optical diagnostics instruments for use during maintenance and inspection of on-wing airfoils in advanced gas turbines.

The complete measurement of the blood velocity and the vein wall deformation is important in order to obtain the wall shear stress distribution in blood vessels. This information would facilitate the diagnosis and treatment of some cardiovascular diseases. In this work, endoscopy has been combined with high speed Particle Image Velocimetry (PIV) to obtain the flow velocity inside a transparent vessel model and with digital holography to measure the vessel wall deformation. The use of endoscopes presents different advantages: they allow the simultaneous illumination and imaging of the object under inspection; the endoscopes can be moved as close as required and can be located anywhere to observe different regions. They can be used for observing inside opaque vessels in an oblique way, where the image perspective distortion can be corrected numerically. High speed PIV and endoscopic PIV have been applied to evaluate the influence of an antithrombotic filter in the velocity field inside an inferior vena cava (IVC) model. Endoscopic digital holography has been developed to measure the wall deformation in vessel models with steady and pulsatile flows. The models present different flexibility and opacity grades. Both the vessel model and the endoscope end are immersed in a refractive index matching liquid in order to avoid distortions.

The eardrum or Tympanic Membrane (TM) transfers acoustic energy from the ear canal (at the external ear) into mechanical motions of the ossicles (at the middle ear). The acousto-mechanical-transformer behavior of the TM is determined by its shape and mechanical properties. For a better understanding of hearing mysteries, full-field-of-view techniques are required to quantify shape, nanometer-scale sound-induced displacement, and mechanical properties of the TM in 3D. In this paper, full-field-of-view, three-dimensional shape and sound-induced displacement of the surface of the TM are obtained by the methods of multiple wavelengths and multiple sensitivity vectors with lensless digital holography. Using our developed digital holographic systems, unique 3D information such as, shape (with micrometer resolution), 3D acoustically-induced displacement (with nanometer resolution), full strain tensor (with nano-strain resolution), 3D phase of motion, and 3D directional cosines of the displacement vectors can be obtained in full-field-ofview with a spatial resolution of about 3 million points on the surface of the TM and a temporal resolution of 15 Hz.

Understanding of the human hearing process requires the quantification of the transient response of the human ear and the human tympanic membrane (TM or eardrum) in particular. Current state-of-the-art medical methods to quantify the transient acousto-mechanical response of the TM provide only averaged acoustic or local information at a few points. This may be insufficient to fully describe the complex patterns unfolding across the full surface of the TM. Existing engineering systems for full-field nanometer measurements of transient events, typically based on holographic methods, constrain the maximum sampling speed and/or require complex experimental setups. We have developed and implemented of a new high-speed (i.e., > 40 Kfps) holographic system (HHS) with a hybrid spatio-temporal local correlation phase sampling method that allows quantification of the full-field nanometer transient (i.e., > 10 kHz) displacement of the human TM. The HHS temporal accuracy and resolution is validated versus a LDV on both artificial membranes and human TMs. The high temporal (i.e., < 24 μs) and spatial (i.e., >100k data points) resolution of our HHS enables simultaneous measurement of the time waveform of the full surface of the TM. These capabilities allow for quantification of spatially-dependent motion parameters such as energy propagation delays surface wave speeds, which can be used to infer local material properties across the surface of the TM. The HHS could provide a new tool for the investigation of the auditory system with applications in medical research, in-vivo clinical diagnosis as well as hearing aids design.

An interferometer for measuring dynamic properties of the in vivo tear film on the human cornea has been developed. The system is a near-infrared instantaneous phase-shifting Twyman-Green interferometer. The laser source is a 785 nm solidstate laser; the system has been carefully designed and calibrated to ensure that the system operates at eye safe levels. Measurements are made over a 6 mm diameter on the cornea. Successive frames of interferometric height measurements are combined to produce movies showing both the quantitative and qualitative changes in the topography of the tear film surface and structure. To date, measurement periods of up to 120 seconds at 28.6 frames per second have been obtained. Several human subjects have been examined using this system, demonstrating a surface height resolution of 25 nm and spatial resolution of 6 μm. Examples of features that have been observed in these in preliminary studies of the tear film include: post-blink disruption, evolution, and stabilization of the tear film; tear film artifacts generated by blinking; tear film evaporation and break-up; and the propagation of foreign objects in the tear film. This paper discusses the interferometer design and presents results from in vivo measurements.

Spatial carrier interferometry is a well-known single frame wavefront phase measuring technique. In this technique a large relative tilt is placed between the test and reference beams producing a high frequency carrier fringe pattern which is modulated by the desired measurement wavefront. Implementation of spatial carrier interferometry is relatively easily accomplished on most advanced laser interferometers. Since it is a single frame technique, it provides robust vibration immunity, enabling measurements involving long paths or mechanically decoupled elements as well as metrology into vacuum chambers and overall environmental immunity. One of the major limitations of this technique is the degradation in measurement accuracy resulting from the large wavefront tilt applied between the test and reference beams. As a result of the large relative beam angle, the test and reference beams do not follow exactly the same path through the interferometer, resulting in what is generally known as retrace error. In this paper an automated calibration technique is introduced which determines the retrace error in a measurement setup without the use of a calibration artifact. This technique works well when measuring both flat and spherical test surfaces. In both cases, the difference between the calibrated wavefront and the wavefront measured on-axis with temporal phase shifting is less than .05 waves. This process allows nanometer-level measurement of precision optics even in difficult environments.

Deflectometric methods have been studied for more than a decade for slope measurement of specular freeform surfaces through utilization of the deformation of a sample pattern after reflection from a tested sample surface. Usually, these approaches require two-directional fringe patterns to be projected on a LCD screen or ground glass and require slope integration, which leads to some complexity for the whole measuring process. This paper proposes a new mathematical measurement model for measuring topography information of freeform specular surfaces, which integrates a virtual reference specular surface into the method of active fringe reflection photogrammetry and presents a straight-forward relation between height of the tested surface and phase signals. This method only requires one direction of horizontal or vertical sinusoidal fringe patterns to be projected from a LCD screen, resulting in a significant reduction in capture time over established methods. Assuming the whole system has been precalibrated during the measurement process, the fringe patterns are captured separately via the virtual reference and detected freeform surfaces by a CCD camera. The reference phase can be solved according to the spatial geometric relation between the LCD screen and the CCD camera. The captured phases can be unwrapped with a heterodyne technique and optimum frequency selection method. Based on this calculated unwrapped-phase and that proposed mathematical model, absolute height of the inspected surface can be computed. Simulated and experimental results show that this methodology can conveniently calculate topography information for freeform and structured specular surfaces without integration and reconstruction processes.

This study defines measurements of three-dimensional rigid-body shapes by using a fiber optic Lloyd’s mirror. A fiber optic Lloyd's mirror assembly is basically a technique to create an optical interference pattern using real light point sources and their images. The generated fringe pattern thanks to this technique is deformed when projected on an object's surface. The deformed fringe pattern containing information of the object's surface profile is captured by a digital CCD camera. The two-dimensional Fourier transformation is applied to the image, which is digitized with a frame grabber card. After applying a band-pass filter to this transformed data in its spatial frequency domain, the twodimensional inverse Fourier transform is applied. Using the complex data obtained by the inverse Fourier transform, the phase information is determined. A phase unwrapping algorithm is applied to eliminate discontinuities in the phase information and to make the phase data continuous. Finally, the continuous data determines the depth information and the surface topography of the object. It is illustrated for the first time that the use of such a fiber optic Lloyd's system increases the compactness and the stability of the fringe projection system. Such a fiber optic Lloyd’s system which provides an accurate non-contact measurement without contaminating and harming the object surface has a wide range of applications from laser interference lithography (LIL) in nano-scale to macro-scale interferometers.

Usage of transparent objects has been increased with technological development of optical structure in display industries and micro optical component in MEMS industries. Their optical characteristics highly depend on the materials and the micro structures. When the optical measurement methods are used for dimensional quality control in their manufacturing, polarization change problem causes the measurement difficulties due to low sensitivity to measurement signals and high sensitivity to noise signals. Interferometry is one of the most promising optical surface measurement techniques. In conventional symmetric interferometers, as the intensities of the reflected lights from the reference mirror and the object are much different, it results in low contrast of interference fringes and low accuracy of dimensional measurement. In this paper, to solve this problem, an asymmetric PFSI(Polarization based Frequency Scanning Interferometer) is proposed using asymmetric polarimetric method. The proposed PFSI system controls the polarization direction of the beam using polarizer and wave plate with conventional FSI system. By controlling the wave plate, it is possible to asymmetrically modulate the magnitude of object beam and reference beam divided by PBS. Based on this principle, if target object consists of transparent parts and opaque parts with different polarization characteristics, each of them can be measured selectively. After fast Fourier transform of the acquired interference signal, the shape of object is obtained from OPD(Optical Path Difference) calculation process. The proposed system is evaluated in terms of measurement accuracy and noise robustness through a series of experiment to show the effectiveness of the system.

Digital Speckle Pattern Interferometry (DSPI) has been applied to measure shape of solid rough objects. A two wavelength setup with one single recording has been applied. Spatial Phase Shifting techniques, with different carrier fringes for each wavelength, have been used in order to produce a spatial multiplex. Selecting each aperture image in the Fourier plane, the amplitude and the phase of the object beam is obtained for each wavelength. The subtraction of those waves produces a wrapped phase map that can be considered a contour line map for a synthetic wavelength. The technique has been applied in different material and the visibility of the fringes is observed. The possibilities and limits of the technique have been analyzed.

In this publication we give a brief introduction into the field of Computational Shear Interferometry (CoSI), which allows for determining arbitrary wave fields from a set of shear interferograms. We discuss limitations of the method with respect to the coherence of the underlying wave field and present various numerical methods to recover it from its sheared representations. Finally, we show experimental results on Digital Holography of objects with rough surface using a fiber coupled light emitting diode and quantitative phase contrast imaging as well as numerical refocusing in Differential Interference Contrast (DIC) microscopy.

Scientific articles focusing on fabrication of micro-components often evaluate their optical performances by techniques such as scanning electron microscopy or surface topography only. However, deriving the optical characteristics from the shape of the optical element requires using propagation algorithms. In this paper, we present a simple and intuitive method, based on the measurement of the intensity point spread function generated by the micro-component. The setup is less expensive than common systems and does not require heavy equipments, since it requires only a microscope objective, a CMOS camera and a displacement stage. This direct characterization method consists in scanning axially and recording sequentially the focal volume. Our system, in transmissive configuration, consists in the investigation of the focus generated by the microlens, allowing measuring the axial and lateral resolutions, estimating the Strehl ratio and calculating the numerical aperture of the microlens. The optical system can also be used in reflective configuration in order to characterize micro-reflective components such as molds. The fixed imaging configuration allows rapid estimation of quality and repeatability of fabricated micro-optical elements.

An optical system capable of simultaneously grabbing three phase-shifted interferometric images was developed for dynamic temperature field measurements outside of a thin flame. The polarization phase shifting technique and a Michelson interferometer that is coupled to a 4-f system with a Ronchi grating placed at the frequency plane are used. This configuration permits the phase-shifted interferograms to be grabbed simultaneously by one CCD. The temperature field measurement is based on measuring the refraction index difference by solving the inverse Abel transform, which requires information obtained by the fringe order localization. Experimental results of a dynamic event are presented varying in time.

Speckle interferometry with CO2 laser (10 micrometers) and microbolometer array has been developed and the final outcome is a mobile interferometer. The long wavelength allows to measure large deformations and is well immune against external perturbations, so as it can be used in field conditions. The technique is based on specklegram recording on the microbolometer array. The background of the specklegram is constituted by the thermal image of the object. Consequently the technique allows simultaneous observation of deformation and temperature difference when an object undergoes a given stress. We show several applications in aerospace nondestructive testing.

Phase retrieval techniques based on the Transport of Intensity Equation (TIE) use a sequence of through-focus intensity images in order to recover the phase information. Classically, the capturing of these images have been made using equally spaced plane separations. Recently, it has been shown that the phase retrieval techniques based on TIE can be carried out using unequally plane separations. In this work we compare quantitatively the phase reconstruction of various TIE solvers using the equal and unequal plane separation strategy.

The Navy Precision Optical Interferometer is an astronomical optical interferometer operating near Flagstaff, Arizona. A joint program between the United States Naval Observatory, the Naval Research Laboratory and Lowell Observatory, it has historically been involved in space imagery and astrometry. More recent work has pushed for the addition of more baselines. It is currently capable of co-phasing 6 elements, so the commissioning of additional baselines requires ease of use and reconfigurability. At the time of this publication, a seventh station has been added and the final commissioning work on an eighth and ninth station are being completed. These last two stations will increase the longest baseline to 435 meters. This paper discusses the work to date on adding these stations and provides details on increased capabilities.

3-D shape measurement systems by contactless method are required in the quality inspections of metal molds and electronic parts in industrial fields. A grating projection method with phase-shifting method has advantages of high precision and high speed. Recently, the size of a BGA (ball grid array) becomes smaller. So the pitch of a grating pattern projected onto the specimen should be smaller. In conventional method, fringe pattern is projected using an imaging lens. The focal depth becomes smaller in the case of reduced projection. It is therefore difficult to project a grating pattern with small pitch onto an object with large incident angles. Authors recently proposed a light source stepping method using a linear LED device. It is easy to shrink the projected grating pitch with a lens because this projection method does not use an imaging lens. The pitch of the projected grating depends on the width of the light source. There is a limit to shrink the projected grating pitch according to the size of the LED chip. In this paper, a small pitch fringe projection method with multiple linear fiber arrays for 3D shape measurement is proposed. The width of the fiber array is 30μm. It is one digit smaller than the width of the LED chip. The experimental result of 3-D shape measurement with small pitch projection with large incident angles is shown.

In this paper, the novel technique for investigating the quality of glass bottle by using digital in-line holography (DIH) has been proposed. In our experimental setup, the collimated beam of short coherent laser diode with wave length of 635 nm incident on a glass bottle. Then, the image bearing reflected beam consisted of quality profile of the glass bottle has been recorded on a CMOS camera. By using the experimental results and numerically reconstructed images, the defects inside the glass bottle can be detected and the curvature radius of the bottle has been found. Our technique may be used for glass bottle inspection in the glass bottle making industry.

A Michelson wavemeter was developed to test the accuracy and give traceability to the wavelength of external cavity diode lasers. These lasers were stabilized using a Littrow configuration and an iodine gas cell as frequency reference, and they will be used as light sources in the assembly of a new interferometric system for gauge block calibration. Previously, the uncertainty evaluation of the Michelson wavemeter with a Vernier counter had to be made, in which, as it is usual, the counting set starts and stops when the interference phases of the reference and unknown wavefronts coincide.

The study of cells-substrate interaction became a stringent subject in the past decades, since an increasing variety of new materials and methods have been involved in tissue engineering or implants techniques. The investigation of this interaction using optical methods is a challenge, especially since these substrates are not optically polished. Due to their roughness in the micrometric or submicrometric range, the polymeric substrates offers good conditions for cells adhesion, but the characterization of cells properties can be hindered. In this study, we use Polypyrrole thin films, acting as substrates for cultured osteoblast-like MG63 cells having applications in tissue engineering for in vivo-like scaffolds. As characterization technique, we chose digital holographic microscopy, a single-shot technique, to obtain quantitative information about the sample features in a plane perpendicular to the substrate. Different parameters were tested in the experimental setup with the aim of finding the optimal conditions for details visualization. The reconstructed 3D images were filtered using a combination of analytical and implicit functions from MATLAB to exclude small/large objects, which correspond to Polypyrrole droplets to clearly identify the cells contour for quantitative measurements regarding their dimensions. These data were correlated with the effects on osteoblasts viability and differentiation. Also, the thickness and the refractive index of the substrate were determined using the decoupling procedure.

Video borescopes are widely used for turbine and aviation engine inspection to guarantee the health of blades and prevent blade failure during running. When the moving components of a turbine engine are inspected with a video borescope, the operator must view every blade in a given stage. The blade counting tool is video interpretation software that runs simultaneously in the background during inspection. It identifies moving turbine blades in a video stream, tracks and counts the blades as they move across the screen. This approach includes blade detection to identify blades in different inspection scenarios and blade tracking to perceive blade movement even in hand-turning engine inspections. The software is able to label each blade by comparing counting results to a known blade count for the engine type and stage. On-screen indications show the borescope user labels for each blade and how many blades have been viewed as the turbine is rotated.

A novel method for holographic femtosecond laser parallel processing is proposed, which can suppress the interference of zero order light effectively and improve the energy utilization rate. In order to blaze the target pattern to the peak position of zero-order interference, a phase-only hologram containing digital blazed grating are designed and generated, The energy of the target pattern can be increased to 5.297 times in theory. In addition, by subsequently increasing the phase of divergent spherical wave, the focal plane of the target pattern and the plane of multi-order diffraction beam resulted from pixelated structure of the spatial light modulator (SLM) can be separated. Both the high pass filter and aperture are used to eliminate the influences of zero-order light and multi-order interferential patterns simultaneously. A system based on the phase-only SLM (with resolution of 1920*1080) is set up to validate the proposed method. The experimental results indicate that the proposed method can achieve high quality holographic femtosecond laser parallel processing with a significantly improved energy utilization rate.